Paramagnetic self-assembled nanoparticles as supramolecular MRI contrast agents

Nanometer-sized materials offer a wide range of applications in biomedical technologies, particularly imaging and diagnostics. Current scaffolds in the nanometer range predominantly make use of inorganic particles, organic polymers or natural peptide-based macromolecules. In contrast we hereby report a supramolecular approach for the preparation of self-assembled dendritic-like nanoparticles for applications as MRI contrast agents. This strategy combines the benefits from low molecular weight imaging agents with the ones of high molecular weight. Their in vitro properties are confirmed by in vivo measurements: post injection of well-defined and meta-stable nanoparticles allows for high-resolution blood-pool imaging, even at very low Gd(III) doses. These dynamic and modular imaging agents are an important addition to the young field of supramolecular medicine using well-defined nanometer-sized assemblies.

Target-specific paramagnetic and superparamagnetic micelles for molecular MR imaging

Treatment of disease can only be effective when timely and accurate diagnosis of the pathology is achieved. More precise diagnosis can be accomplished if the underlying molecular processes involved in the pathology can be imaged in vivo. This is the field of molecular imaging, which aims to visualize cellular function and molecular processes in living organisms in a non-invasive way. With that aim, molecular markers are specifically targeted by imaging contrast agents. Molecular MRI needs powerful targeted contrast agents. For that purpose, target-specific gadolinium-containing paramagnetic and superparamagnetic, iron oxide-based micelles have been developed. Micelles are lipid-based nanoparticles which are biocompatible and carry a high payload of MR contrast-generating agent. The coupling of high-affinity ligands makes the micelles target-specific. Additionally, this lipid-based micelle platform allows for incorporation of contrast generating molecules for other imaging modalities, e.g., fluorescence or nuclear imaging. This permits applications for multiple imaging modalities, making micelles a highly versatile contrast agent.

Development and evaluation of a cetuximab-based imaging probe to target EGFR and EGFRvIII

BACKGROUND AND PURPOSE

The epidermal growth factor receptor (EGFR) is overexpressed in a significant percentage of human malignancies and its expression is associated with tumour aggressiveness and treatment resistance. The monoclonal antibody cetuximab (IMC-C225) blocks the ligand-binding domain of EGFR with high affinity, preventing downstream signalling resulting in tumour growth inhibition. We developed and characterized a novel imaging probe using Oregon Green 488 labelled cetuximab to evaluate its usage as an imaging agent to target EGFR.

MATERIALS AND METHODS

Cells with varying expression levels of EGFR or a mutant form of EGFR, called EGFRvIII, were used for in vitro validation. The in vivo binding of labelled cetuximab to EGFR was also assessed ex vivo on tumour material.

RESULTS

The development of Oregon Green 488 labelled cetuximab was successful, demonstrating binding to both EGFR and EGFRvIII in vitro. Accumulation was also found in vivo, which was confirmed by histopathology using anti-EGFR antibodies. However, significant mismatch highlights differences between drug delivery in vivo, and cell expression levels of EGFR.

CONCLUSIONS

The monoclonal antibody cetuximab represents a promising probe to evaluate the biologic and pharmacokinetic effects of in vivo cetuximab binding to EGFR. It not only visualizes the presence of the wild type EGFR, but also the presence of the mutant EGFRvIII.